If you have any doubt as to why we think the UK's Department for International Development should prioritise disability, look no further than the situation of Esther Cheelo.
Blind, elderly and with difficulty walking, Esther has for years relied upon a child to walk her into the scrubland near her home in Zambia to find a place to relieve herself, a humiliating and sometimes dangerous experience.
"They would lead me to the thorns and I would get cuts on my ankles and legs. Sometimes, the child would not see a ditch and I would fall," she recalled to a WaterAid programme officer.
But then, with the help of a WaterAid partner organisation, her village got a water point and toilets for the first time. Her family, drawing on the example of another household, built her an accessible toilet and added a guide rope, which Esther can now find and follow on her own.
With the new water point, rationing has eased, and the village's women and children no longer have to walk long distances to fetch drinking water.
"Before they brought water, I could bathe once a month. I was smelling. That is the truth," she confided. "People never used to eat with me because I was dirty and smelling. Now everyone can eat together as I am no longer dirty."
Consider the change: Esther no longer has the humiliation of having to wait for help to relieve herself.
The children who used to help her to the toilet are now more able to focus on their education or to helping parents at home. She is now able to participate more fully in the events of her village, and put forward the needs of other disabled people.
All this, from just one basic toilet, a guide rope, and a nearby water point.
The toilet that changed Esther's life (Photo by Jane Wilbur, WaterAid)
International development that meets the needs of disabled people does not need to be complex, expensive or difficult. It just needs to be front of mind.
I appeared before the International Development Select Committee last week to talk about how very basic the approach can be to include disabled people in aid programming. The WHO estimates that 15% of the world's population is disabled. That is over one billion people.
The principle required couldn't be simpler: include everyone in the community. Not just the 85% of people who are able. Not just the healthy children brought out by the parents too embarrassed to acknowledge the disabled child inside, as I have seen and heard first-hand in my travels. Everyone, everywhere.
There are some modest costs associated with this. But consider the costs of not doing so. Disabled children cannot go to schools without accessible toilets, which means that they miss out on an education and won't reach their full social and economic potential. Disabled girls will drop out at puberty if they cannot manage their periods at school with a private place to wash and dispose of used pads. Families of disabled people will spend time fetching water and helping their loved one to the toilet, time away from work or schooling.
Esther was part of our Undoing Inequity project in Uganda and Zambia, where we have examined how programmes on water, sanitation and hygiene can be made more accessible. This has been done in partnership with SHARE, a research consortium funded by the Department for International Development, with an eye to taking it larger scale elsewhere.
It has been a revealing exercise. We have found that the costs of accessibility are, by and large, reasonable. Research conducted in Tanzania by the water and engineering development centre at Loughborough University shows that designing a school latrine that is accessible to disabled people adds less than 3% to the total cost of building. Ramps, wider entrances, simple handrails or movable wooden toilet seats are all low-tech and low-cost but effective. A rainwater harvesting jar placed outside a disabled person's home can provide an easy-to-reach additional source of safe water.
Disabled people remain the most marginalised of the poor, and the most likely to be left out of global efforts to reduce extreme poverty.
If we really want everyone, everywhere to access water and sanitation by 2030, we need to reach out to make sure even those disabled children and grandmothers previously unseen in their communities are heard and included.